1. Field of the Invention
The present invention relates to a slurry recycling system for a chemical mechanical polishing (CMP) apparatus, and a method of the same, for recycling slurry used when polishing wafers etc. in a CMP apparatus.
2. Description of the Related Art
FIG. 9 is a schematic view of the configuration of a CMP apparatus.
As shown in FIG. 9, the CMP apparatus is provided with a platen 100 on the surface of which is attached a polishing pad 101 and a carrier 200 for holding a wafer W.
The wafer W is pressed against the top of the polishing pad 101 by the carrier 200. In this state, the platen 100 and carrier 200 are rotated relative to each other. Slurry S is continuously supplied from a slurry feed apparatus 300 to the top of the polishing pad. As a result, the precision of polishing and polishing rate of the wafer W are improved.
The slurry S used for the CMP apparatus, as explained in detail later, is comprised of metal oxides etc. of a primary particle size of not more than 10 .mu.m dispersed in water or an organic solvent. If used for polishing a wafer W in a CMP apparatus, the state of agglomeration of the primary particles of the slurry S changes and the state of dispersion of the slurry S fluctuates from its initial value.
Accordingly, if such once used slurry S is reused in the CMP apparatus, the polishing rate will vary, the wafer W will not become the desired flatness, or large agglomerations of particles will cause scratching of the wafer W.
Therefore, in the past, the once used slurry S was received by a waste liquor receiver 110, stored in a waste liquor tank 120, then completely disposed of. Accordingly, a huge amount of the slurry came to be used. This became a major cause behind higher costs in polishing work.
As opposed to this, recently, the method has been proposed of filtering the once used slurry S using a filter, then reusing it.
The filter, however, becomes clogged in a short time and then has to be replaced with a new one.
Accordingly, it was necessary to stop the CMP apparatus when replacing the filter. This caused a reduction in the operating rate of the CMP apparatus. Further, a stable filtration action could not be achieved right after the filter was replaced with a new one. The polishing work consequently might be hindered during that time.